No. 2.] EARLY DEVELOPMENT OF AMBLYSTOMA. 375 



If, when the blastopore has become horse-shoe shaped, punc- 

 tures are made on the outside at either extremity, the extra- 

 ovates generally (7 eggs) lie at the side of the slit-like blasto- 

 pore, or are carried in (2 eggs). In 9 eggs markings at the 

 ventral lip of the blastopore, when it had become circular, were 

 found at the posterior end of the embryo. 



The observations of Morgan and Tsuda ('94) show that the 

 same is true in Rana; and further, if the puncture is made at 

 the center of the vegetative pole, it later lies in the tail region 

 of the embryo. Often it happens that the extra-ovate is in- 

 folded or overgrown. 



In 13 cases, when the blastopore had become crescentic, 

 punctures were made at the equator, on the opposite side of 

 the &%g. The extra-ovates later occupied a position on the 

 ventral side of the &g%, beyond the caudal end of the embryo. 

 Roux ('88®) states that a defect here is later found at the caudal 

 end of the embryo. 



4. The Embryonic Area. 



The older idea of von Baer was that the Frog's egg, like that 

 of the other vertebrates, could be considered as made up of 

 two parts, the germinal and nutritive, represented by the dark 

 and light hemispheres respectively. 



Pfluger (83) holds that the embryo develops largely in the 

 white hemisphere of the &%g, but thinks it probable that the 

 anterior portion of the medullary plate arises from the black 

 hemisphere. 



Schultze ('88), by following the path of certain local defects 

 found on the surface of the ^gg, concludes that the embryo is 

 formed entirely in the dark hemisphere. 



Roux ('88) concludes from the fate of a number of artificial 

 markings produced by a hot needle that the embryo develops 

 almost exclusively from the inferior hemisphere. Hertwig ('92), 

 from a study of abnormal forms, reaches practically the same 

 conclusion. 



Morgan and Tsuda ('94) state that they in the main point 

 agree with Pfluger and Roux. 



